Oh oh... had that happen once. Might not be the poo pyramid under the toilet, but a clog of TP at the exit. Drove back from Myrtle Beach like that, dumped every chemical I could down the toilet to hope to break up the clog. 2 days of road to get home and the clog was still strong.
Had to hunker down and do it the bad way... poked a hanger up there a couple of times and hoped to get the hose back on before it all came a rushing while DW sat inside giggling her butt off. Thank god I had the foresight to wear clothes and an old pair of shoes that I wasn't worried about ever wearing again. Strongly suggest doing this at an out of the way dump station and not at the park campsite.
Side note: advised her that she needs to be more careful about TP usage, or she'll be the one with the hanger next time. No messes since.